One known analgesic electrotherapy technique is transcutaneous electrical nerve stimulation, commonly called TENS (the acronym). The latter consists in exciting sensitive afferent paths by means of electrodes placed on the skin, so as to lessen or block the pain (Gate control theory, stimulation of the production of endogenous analgesics). This technique is widely known (1,2,3) and regularly used to combat various types of pain.
Most migraines and tension headaches spread on to the surface of the front half of the cranium. The afferent path of this pain is located in the trigeminal nerve (Trigeminus nervus), shown in FIG. 1, which has three branches: the ophthalmic branch 1, the maxillary branch 4 and the mandibular branch 5. The afferent path of the above-mentioned pain is more precisely the upper branch of the trigeminal nerve 1 which is also called Willis' ophthalmic nerve.
This nerve divides into two branches on the forehead: the internal frontal (or supratrochlear) nerve 2 and the external frontal (or supraorbital) nerve 3.
Thus the application of analgesic electrotherapy of a TENS type to the supraorbital and supratrochlear nerves allows one to combat the pain of most migraines and tension headaches as described in the medical literature (4, 5, 6, 7).
International application WO 2006/063417 A1 belonging to the Applicant describes a device for electro-inhibition of the facial muscles marketed under the name of Safetox® Beauty, which applies electric currents via a bipolar electrode placed on the forehead. The two poles of the electrode are part of a single structure comprising a piece of cloth acting as a support. The electrodes are covered with a self-adhesive conductive gel on their inner surface which is intended to be in contact with the skin. They are in the form of two conductive silvered zones that impregnate the piece of cloth, which is therefore also conductive on its outer surface in contact with the electricity supply pads. This device is used without causing significant pain. This is possible because the electrode of said device has been designed to be of a very small size. Typically the two poles of the electrode have a maximum surface area of between 100 and 200 mm2 and they are separated by a distance of 4 to 8 mm. The relevant surface of the periosteum is very small and the current does not penetrate the tissues very deeply.
Thanks to its limited surface area, this type of electrode allows an action only on the supratrochlear (internal frontal) nerves but has no effect on the supraorbital (external frontal) nerves. Therefore it does not entirely fulfil the criteria of effectiveness for an analgesic electrotherapy treatment of a TENS type in the case of migraines and headaches.
When a wider electrode of the usual form is used to excite the afferent paths of the supraorbital (external frontal) nerves, the currents generated by the Safetox® Beauty cause pains, which make the above-mentioned treatment unbearable.
Document WO 2006/051370 A1 relates to an electrotherapy device applied in particular to the treatment of migraines and other headaches, neuralgias, ophthalmic shingles, Arnold's syndrome etc. This is a device comprising at least one electrode for the application of a treatment current and a means of control. The latter comprises at least a means of activation for initiating the provision of a predetermined current profile in its various parameters, in particular the intensity, and a means of stabilisation which, when it is activated, causes a modification of said current profile by restricting the intensity of the current to its value at the moment of activation of said means of stabilisation. This would therefore limit the risk of too intense a pain for the patient during the application of a predetermined current profile thanks to the means of stabilisation that the patient himself can activate. The electrodes are four in number and associated laterally two by two, each path having one supraorbital frontal electrode and a zygomatic electrode. This arrangement corresponds to the surface projection of the trifurcation of the trigeminal nerve on the surface at the zygomatic position and the passage of its ophthalmic branch over the supraorbital ridge. The cloth electrode support comprises in particular a strip equipped with two sliding sleeves to allow the adjustment of the position of the electrodes at the level of the supraorbital ridges, which allows the specific morphological details of each patient to be taken into account.